The present invention concerns a dressing of the type comprising a skin friendly pressure-sensitive continuous or discontinuous adhesive layer, which is coated on one side with a non-adhesive flexible polymer film, optionally with a flexible foam layer interposed between the film layer and the adhesive layer, and which is optionally coated on the other side with a removable release layer.
Dressings of the above-mentioned type are extensively used for the treatment of wounds, in particular cronic wounds, burns and surgical wounds. Dressings of the above-mentioned type are also used for the treatment of blisters, minor wounds and chafe wounds, as well as prophylactically to avoid the same, e.g. in connection with the practice of sports or manual labor and the like, where the skin areas, such as heels, elbows, knees and palms of the hand are subject to particularly severe stresses which easily give rise to the above-mentioned minor injures. Dressings of the above-mentioned type continue to find new fields of application. It may for example be mentioned that such dressings have also been found useful as a transcutaneous dosing means for the dosing of various medicaments, such as hormones or nicotine.
Thus, a large number of products of the above-mentioned type are known. The products most used are the so-called liquid absorbing bandages, e.g. hydrocolloid plasters and hydrogel plasters.
Hydrogel bandages consist of a liquid absorbing crosslinked polymer, such as collagen, polyvinyl alcohol and gelatine, as well as of a non-adhesive watertight film having a low water vapor permeability arranged on the side of the bandage which is not intended to face the skin of the patient.
A hydrogel bandage contains a large amount of water already prior to use. In the cases where the bandage is approximately saturated with water, the bandage is frequently not adhesive and must therefore be secured to the skin in another manner, e.g. by means of a plaster. An example of this is the so-called 2ND SKIN.RTM. dressing which is commercially available from Spenco Medical Ltd., U.K. Other hydrogel bandages having a lower content of water exhibit excellent adhesive properties. Certain modified gellable polymers, however, are capable of maintaining a reasonably good adhesive capability, even when they are essentially saturated with water.
Hydrogel bandages are known e.g. EP Patent Applications 97846 and 415183, SE Published Application 365 410, WO Patent Application 88/6894 and U.S. Patent Specification 4 093 673.
Hydrocolloid plasters normally consist of
(a) an adhesive material consisting of PA0 (b) a non-adhesive watertight film arranged on the side of the bandage which is not intended to face the patient's skin. PA0 (a) a physically cross-linked elastomer in the form of one or more styrene olefin styrene block copolymers or ethylene propylene block copolymers, PA0 (b) a hydrocarbon adhesive resin in the form of a polymer or copolymer of cyclopentadiene, dicyclopentadiene, .alpha.-pinene and/or .beta.-pinene, PA0 (c) an antioxidant, PA0 (d) optionally an oil extender consisting of one or more mineral oils, and PA0 (e) an elastomer polar plasticizer, such as for example an ester of a polyethylene glycol or polypropylene glycol, or an ester of a di- or polybasic carboxylic acid with a preferably aliphatic alcohol, as well as PA0 a) The polymer material for the uppermost film layer is dissolved in a suitable solvent, and optional additives are admixed, following which the mixture is applied in a thin layer to a suitable carrier material which easily releases the finished polymer and is dried. PA0 b) The polymer material for the lowermost film layer is dissolved in a suitable solvent, and optional additives are admixed, following which the mixture is applied (optionally in a pattern), on the uppermost film and is dried. PA0 c) An adhesive material is applied to the film layer, with a foam layer optionally interposed between the adhesive material and the film material, and the adhesive material is optionally covered with a removable release layer. PA0 d) The skin sheets are punched after optional bevelling, e.g., as mentioned in DK Published Application 154 747.
(i) a continuous phase containing an adhesive and composed of for example an elastomer, a plasticizer for elastomers, a tack promoting resin and optionally an oil based extender as well as an antioxidant, and PA1 (ii) a discontinuous phase dispersed therein and consisting of one or more water soluble or water swellable hydrocolloids, such as starch or cellulose derivatives or other hydrophillic polymers, and
Such a dressing is known e.g. from the DK Patent Specifications 147 034 and 147 035 (corresponding to U.S. Patent Specifications 4 231 369 and 4 367 632). The products mentioned in these consist of an adhesive material consisting of
(I) a continuous phase containing
(II) a phase dispersed in the continuous phase and consisting of one or more water swellable hydrocolloids.
Also other elastomers may occur in known dressings, e.g., natural rubber, synthetic resins of a nature similar to natural rubber and silicone rubbers. Further, polyisobutylene in a suitable molecular weight distribution is also frequently used as an adhesive material and texture imparting component in dressings, e.g. as stated in U.S. Patent Specification 3 339 546.
Other dressings of a similar type are known from NO Published Application 157 686 as well as DK Patent Specifications 154 806, 147 226, 157 899 and 154 747.
Mention should also be made of WO Patent Application 90/01911, and DK Published Application 158 493, which concern bandages that essentially do not contain components which are actively water absorbing. In particular, thin, non-liquid absorbing products are greatly used. Mention may here be made of e.g. the dressing Tegaderm.RTM. which is marketed by 3M, the dressing Bioclosure.RTM. which is marketed by Johnson & Johnson, the dressing Up-Site.RTM. which is marketed by Smith & Nephew, and the dressing Uniflex.RTM. which is marketed by Howmedica.
The thin non-absorbing products are extremely flexible and often transparent. They consist of a non-absorbing adhesive, such as rubber, various acrylates or copolymerisates thereof, polyvinyl ether and synthetic or natural resins and a film cover layer which is frequently watertight, but has a relatively great water vapor permeability. In contrast to the absorbing bandages, this water vapor permeability is very important, because the skin constantly secretes a certain amount of liquid which may give rise to maceration. In case of very suppurating wounds, these thin non-absorbing bandages cannot always be applied successfully.
A development of recent years is the combination of these different types of bandages. For example, also hydro-colloid bandages as thin as 0.3 mm are now available. Such thin hydrocolloid bandages are not always capable of absorbing all the liquid secreted from the skin and possible wounds, and it is thus important that these thin hydro-colloid bandages have a cover film with a reasonably great water vapor permeability. This water vapor permeability, as mentioned before, has no significant importance for the thicker hydrocolloid bandages of e.g. 1.0 mm or more, since these bandages are essentially capable of absorbing the amount of liquid secreted from the skin and possible wounds.
Another type of bandage consisting of a combination of the above-mentioned types of bandages is the one known from the above-mentioned DK Published Application 157 899, in which the bandage has an adhesive layer consisting of various types of adhesives arranged juxtaposed in a pattern.
DK Published Application 147 226 (corresponding to U.S. Pat. No. 3,982,328) mentions a bandage which comprises an adhesive layer, a film layer and a flexible layer interposed therebetween.
Like the previously mentioned adhesive layers, the adhesive layer may e.g. contain rubber-like elastomers and liquid absorbing hydrocolloid. The foam layer is a non-compressed semi-open cell layer of e.g. polyurethane which, in addition to being flexible, can also be elastic.
The film layer has a water vapor permeable water impermeable flexible polymer film, such as polyurethane.
Such bandages containing a foam layer may have an overall thickness of down to about 0.6 mm.
A common feature of all the above-mentioned bandages is that they are relatively thin, i.e. thinner than 3.0 mm and in particular thinner than 1.0 mm. Furthermore, they are flexible and frequently elastic so that when being used they can be shaped and conform to the bends and shapes of the skin surface.
The elastic property of the bandages is very essential, because it is precisely this property which enables a bandage to conform to the skin upon movements and the like, and moreover the elasticity of a bandage is of great importance for the comfort when using it.
For a bandage to have a sufficient elasticity to satisfy the functional requirements, as stated above, it is essential that each individual one of the constituent layers is sufficiently elastic, since it is the least elastic layer that determines the elasticity of the assembled product.
The elasticity of the non-adhesive film usually determines the elasticity of the entire dressing, in particular in case of the quite thin dressings, because the adhesive mass is relatively more elastic than even the most elastic non-adhesive polymer film.
Foam layers frequently also possess a sufficient elasticity, in particular the non-compressed foam layers. Bandages containing a polymer foam layer are frequently just as elastic as bandages without a foam layer.
The film layer on bandages with a foam layer and bandages without a foam layer, respectively, serve several purposes.
The film layer on bandages having a foam layer serves inter alia to strengthen the foam layer, cf. DK Published Application 147 226, page 5, lines 9-10.
The film layer on bandages without a foam layer, i.e. where the film layer is in direct contact with the adhesive layer, serves to cover the adhesive face facing away from the skin, so that clothes and other objects do not stick to the adhesive.
Whether or not the bandage has a foam layer, the film serves to protect against contaminations and ingress of bacteria, etc. and another essential purpose of the film is to impart a smooth surface to the bandage.
In the use of the bandage, the film is subjected to several wear forces, such as rubbing against clothes or other objects, tension and stretching as caused by the movements of the user, as well as removal of the bandage.
Thus, it is very important that the film has a sufficient strength to resist these external impacts.
It is thus clear that the most important properties of the film are that it must be elastic and wear resistant.
Both the elasticity and strength properties depend upon the composition of the material and the thickness of the film layer, the elasticity of the film decreasing with increasing thickness, and the strength of the film increasing with increasing thickness. Thus, it has been necessary to weigh the desired elasticity and strength properties.
The non-adhesive films in known dressings of the type described in the opening paragraph thus typically have a thickness of 20-40 .mu.m. Films in this thickness range of a material having a reasonable elasticity can thus essentially satisfy the requirements made both of the elasticity and the wear strength.
The film materials most used are different polyurethanes, which are selected in particular because of their excellent elastic properties and possibly water vapor permeability properties, but also other polymer types, in particular elastomers, are used as non-adhesive films in dressings.
The more elastic a film in a given thickness is, the lower hardness the film material has.
The non-adhesive film used for the known dressings thus consists of a polymer material which is relatively soft either per se or after addition of a plasticizer.
The known dressings consisting of a skin friendly pressure-sensitive adhesive layer and a non-adhesive, relatively soft film, optionally with an elastic foam material layer interposed therebetween, thus have a good flexibility, and the known dressings in which the adhesive layer or the sum of the adhesive layer and the foam layer is 2.0 mm or thinner, have a particularly good flexibility and elasticity, so that they can easily conform to the body to provide great comfort in use.
However, the existing dressings have the drawback that after some time they very frequently roll off completely or partly. This drawback is caused by the fact that in addition to the desirable elasticity, the non-adhesive, relatively soft film also exhibits a high friction in particular with relation to skin, leather, plastics and certain fabrics. In case of external forces, such as friction against articles, clothing or other skin surfaces, the edges of the dressing thus work loose and roll up, causing the adhesive layer to turn away from the skin surface to which it is intended to adhere so that instead it sticks to garments and the like, whereby the dressing is easily torn off or rolled up completely or the foam layer is torn to pieces.
This is a long-known problem, but the only known solution proposed is the one mentioned in EP Patent Application 409 587, in which the employed non-adhesive film is embossed in relief so that the bandage surface area offering resistance upon rubbing against another plain surface is significantly diminished. The coefficient of friction between the embossed bandage surface and a given plane surface, e.g. a non-woven fabric surface, is thus unchanged, but since the contact area is reduced, the resulting friction is likewise reduced.
However, the embossed bandage surface only gives rise to reduced friction upon rubbing against plain or approximately plain surface. Rubbing against irregular surfaces, such as certain knitted or woven fabric surfaces, frequently causes the resulting friction to be considerably greater than if the bandage surface was not embossed. Additionally, protruding parts and edges on, e.g., garments or footwear can very easily grip the bosses and thus cause the bandage to be removed.
Furthermore, the embossed areas in the bandage frequently collect dirt and bacteria, which is very inexpedient and inacceptable to the users.
An essential reason why no other solutions have been developed, as far as is known, is presumably that the elastic property of the dressing has been given priority, because lack of said property would involve even easier undesirable removal of the dressing.
In an attempt at solving the above-mentioned problem of friction, the inventors of the present invention tested, polymer materials having a greater hardness than the materials normally used operated as non-adhesive films in a dressing. As might expected, it was found that the surface friction of the non-adhesive film decreased with increasing hardness of the material, but at the same time the elasticity decreased so drastically that the selection of a polymer material having a hardness giving even a tolerably acceptable low value of friction resulted in such an inelastic polymer film that in the employed thicknesses for use for dressings, it would be quite inapplicable. To obtain even a tolerably acceptable elasticity, it was thus found that the film of the higher hardness should be thinner than 10 .mu.m and preferably 5 .mu.m or less.
When testing a dressing consisting of an adhesive layer and a film with a higher hardness in a thickness of 10 .mu.m or less, it was found that the film tore easily in use, because it did not possess a sufficient strength or elasticity to conform to the movements of the skin or to absorb other effects occurring in use, and it was simultaneously found that large areas, in particular edge areas, were torn in use.
It was additionally found that the dressing having the very thin and relatively hard film was significantly more difficult to remove than the known dressings, because the film broke during removal and thus was not capable of holding the adhesive material together, which was left on the skin in major and minor spots.